I have been searching for compatability issues for a laptop running 64 bit Vixta. The lady who bought it doesn't even understand the difference between 32 and 64 bit. I've read where people had no problems to articles where they had all kinds of problems. Supposedly Vista 64 bit has something built into it that somehow lets 32 bit software run on a Vista 64 bit machine, but I had never heard of it. I'm sure you have knowledge about this issue. I have many customers and I have kept them running XP 32 bit because that is all they need and it is supported, at least SP3, until 2014. I do not plan on running anything 64 bit myself until Windows 7 64 bit comes out and there is enough software to warrant the change. Please let me know what you have experienced and or heard about what we are getting into. I am not in a position of running any other operating system than those from Microsoft because my customers are set in their ways and I have all of their systems working so well that I don't hear from most except maybe every other year. Just this one woman who likes to make decisions based on something, maybe her astrology program that she was afraid would not run.
Vista x64 can run any 32 bit program (unless it has a 16 bit installer). It can't run 16 bit programs. The only real advantage of a x64 OS is that it can run more than 4 GB of RAM. 4 is about the most an average person would really need anyway.
Unless they're dealing with huge RAW files in Photoshop, or something analogous, then having more RAM isn't entirely necessary. Even the most hard core of video games rarely take advantage of more than 4 GB of RAM.
Also, there are very few x64 programs, and again they usually don't need the large amount of memory that the architecture provides.
However, there are very few issues running 32-bit software on 64-bit Windows. I know I haven't come across a program yet that's failed to run under Vista 64... and I run 32-bit software exclusively. My point is that if you purchased a computer with 64-bit Vista preinstalled, there is no point in making the effort to downgrade to 32-bit. Most people will never notice the difference.
OP: In x64 versions of Windows, there is a feature called "WOW64" ("Windows on Windows") which provides the necessary libraries and registry redirection needed to run 32 bit windows programs in a 64 bit environment.
The important thing for most people to knwo is:
if you purchased a computer with 64-bit Vista preinstalled, there is no point in making the effort to downgrade to 32-bit. Most people will never notice the difference.
All a user would notice is two icons for Internet Exploder (an x86 and an x64 version), instead of one and that Flash doesn't work with the 64 bit one. That there are two 'Programs' folders - one for 32 bit programs and the other for 64. And that the Properties tab says x64.